For single-color or multicolored printing of a recording medium (for example of a single sheet or a band-shaped recording medium) made of the most varied materials (for example paper or thin plastic or metal films) it is known to generate image-dependent potential images (charge images) on an intermediate image carrier (for example a photoconductor) that correspond to the images to be printed, made up of regions that are to be inked and regions that are not to be inked. The regions of the potential images that are to be inked are made visible with a developer station (inking station) via toner. The toner image is subsequently transfer-printed onto the recording medium.
Toner particles and developer fluid containing carrier fluid can thereby be used for inking of the potential images. The carrier fluid thereby exhibits a resistance of greater than 108 Ohm*cm. Possible carrier fluids are, among other things, silicon oil and hydrocarbons.
A method for electrophoretic fluid development (electrographic development) in digital printing systems is known from WO 2005/013013 A2, for example. A carrier fluid containing silicon oil, with ink particles (toner particles) dispersed therein, is thereby used as a developer fluid. More detail in this regard can be learned from WO 2005/013013 A2 corresponding to U.S. Ser. No. 10/565,250, which is a component of the disclosure of the present application.
The feed of the developer fluid to the intermediate image carrier can occur via an applicator roller to which the developer fluid is supplied by a raster roller at which a chamber scraper is arranged. The use of chamber scrapers for supplying ink is known from offset printing (EP 1 097 813 A2 corresponding to U.S. Pat. No. 6,371,024). The use of a chamber scraper in electrophoretic printing can be learned from WO 2005/013013 A2. A disadvantage of the known chamber scrapers is that the flow of the developer fluid is not directed in a targeted manner. Eddies can therefore occur and air bubbles can be introduced. The filling of the cups of the raster roller additionally occurs without potential assistance, such that the transition of the toner particles to the raster roller is limited. The achievable toner application per surface element is thereby limited, and with this the inking region or the speed of the transition of the developer fluid onto the raster roller, and with this the achievable process speed given constant inking.
The design of a raster roller that works together with a chamber scraper is known from DE 44 08 615 A1. In order to enlarge the shape of the cups of the raster roller, a voltage is applied to the chamber scraper and the raster roller. The raster roller is designed such that the shape of the cups can be altered via an electrical voltage.
Mathes, H. (“Gibt es die optimale Kammerrakel?” part 1 in Flexo+Tief-Druck 1-2003, p. 54-58, January 2003, part 3 in Flexo+Tief-Druck 6-2003, p. 68-71, November 2003) describes the realization of an arrangement made up of raster roller and chamber scraper. In order to press the air out from the cups of the raster roller upon filling with ink, it is proposed to direct the ink over the raster roller under pressure. For this a profile body in the chamber scraper can be arranged adjacent to the raster roller, via which profile body the transport channel for the ink is constricted adjacent to the raster roller.
According to EP 0 727 720 B1, the cleaning of the residual image (that remains after the development of the potential images on the applicator roller) from the applicator roller occurs via a scraper adjoining the applicator roller. However, an elastic coating of the applicator roller that is required for the neighboring image point formation at the intermediate image carrier is quickly abraded with this. To the contrary, if the contact pressure of the scraper is too weak, a low cleaning efficiency is accepted, which leads to memory effects given high print utilization (areal degree of coverage of the print image) since not every point of the applicator roller exhibits the same toner quantity/area after a cycle. The cleaning of the applicator roller can also occur via a cleaning roller with scrapers. Since the toner particles are then drawn towards the surface of the cleaning roller, this leads to high stress on the toner particles at the point of action of the scraper on the cleaning roller. This leads to the agglomeration of toner particles and macroscopic thickenings. If the efficiency of the scraper is insufficient, this leads to film formation on the cleaning roller or to the development of memory effects.